A “valency platform” is a molecule with one or more (and typically multiple) attachment sites which can be used to covalently attach biologically active molecules of interest to a common scaffold. The attachment of biologically active molecules to a common scaffold provides multivalent conjugates in which multiple copies of the biologically active molecule are covalently linked to the same platform. A “defined” or “chemically defined” valency platform is a platform with defined structure, thus a defined number of attachment points and a defined valency. A defined valency platform conjugate is a conjugate with defined structure and has a defined number of attached biologically active compounds. Examples of biologically active molecules include oligonucleotides, peptides, polypeptides, proteins, antibodies, saccharides, polysaccharides, epitopes, mimotopes, drugs, and the like. For example, the biologically active compounds may interact specifically with proteinaceous receptors.
Certain classes of chemically defined valency platforms, methods for their preparation, conjugates comprising them, and methods for the preparation of such conjugates, have been described in U.S. Pat. Nos. 5,162,515; 5,391,785; 5,276,013; 5,786,512; 5,726,329; 5,268,454; 5,552,391; 5,606,047; and 5,663,395. Valency platform molecules comprising carbamate linkages are described in U.S. Pat. No. 6,458,953; and WO 00/34231. Valency platform molecules comprising aminooxy groups are described in U.S. Provisional Patent Application No. 60/138,260, filed Jun. 8, 1999; and PCT/US00/15968.
Polyethylene glycol conjugates are described, for example, in PCT WO 99/45964, published Sep. 16, 1999; U.S. Pat. Nos. 5,672,662; 5,932,462; PCT WO 99/34833; PCT WO 95/34326; and U.S. Pat. No. 5,990,237. Polyether copolymers including linear and dendritic blocks are described in Gitsov et al., Angew Chem. Int. Ed. Engl., 1992, 31:1200-1203. A polyethylene glycol multiblock copolymer as a carrier of the anticancer drug doxorubicin is described in Pechar et al., Bioconjugate Chem., 11:131-139 (2000). A polyethylene glycol copolymer for carrying and releasing multiple copies of peptides is described in Huang et al., Bioconjugate Chem. 9:612-617 (1998). Polyethylene glycol copolymers and their self assembly with DNA are described in Choi et al., J. Am. Chem. Soc., 122:474-480 (2000). Polyether dendritic compounds containing folate residues are described in Kono et al., Bioconjugate Chemistry, 10:1115-1121 (1999).
Direct PEGylation of polypeptides is generally done by attaching to lysine amino groups or other side chain functionality. This often results in a heterogeneous mixture of products and can lead to loss of bio-activity. Thus, there is a need for improved methods of forming multivalent conjugates of biologically active molecules and polyethylene oxide groups.